Why is there a rattling noise coming from the back of my car?

I have a 2012 honda accord it has 28k miles on it and lately when i drive on uneven roads or go into potholes the back of the car where the speaker are rattles a lot very loudly and it's annoying. Always the side of the passenger seat rattles. Any ideas on why this can be before i take it to the dealer to check it out?

See if you can make the rattle by tapping or hitting things with your hand. Is it the Seat buckle touching against plastic somewhere or could there be something in the car that is causing it. Sometimes the tray in the rear can work loose & vibrate too.

It's most likely a bad shock (rubber bushing) on that side of the car that's rattling.